The easiest way to go about it is to just load up Oblivion.esm in the CS and create a new worldspace and then change the chargen quest/script to start you off in your new world. You can find the details on the CS wiki. This http://cs.elderscrolls.com/constwiki/index.php/WorldBuilding_101 will walk you through the steps, though you can ignore all the stuff about fractal terrain (unless that's what you want) and just create your worldspace using the heightmap editor or landscape editor (if it is really small). It's really quite easy to set up and only takes a few minutes once you know what you're doing.
I think what you're trying to get at, however, is using a 'blank' esm. You can do this just by not loading Oblivion.esm when you start the CS but you're in for a long, long haul doing it this way. If you go this route, you'll have to create objects for all of the assets that you want to use and I don't see any advantage in doing it this way, tbh. Using Oblivion as a master imposes absolutely no penalties or restrictions so there is no reason not to use it.
Thanks!
Ill look into this later this week if things settle down.
All I want to do is create a smaller more basic rpg. Kind of like how Zelda only has 3 swords and 2 different potions. This would no doubt be more complex since it will use everything Oblivion has without really changing anything about the core game really. Same races, weapons classes, game play mechanics ect.
I want to create the terrain by hand and just have fun with the idea.
I wonder how much of a step back going from the Geck to Tes4 is going to be >.>